A standard desktop computer keyboard contains 100 or more keys. The keyboard may be used to encode many more symbols than it has keys, including letters, capital letters, accented letters, digits, punctuation symbols, and functional symbols such as symbols to encode cursor movement, character deletion, or shortcut access to the internet. Therefore, many of the keys are typically called on to encode more than one symbol. As the number of different functions a computer keyboard needs to perform is increasing, the number of keys on a typical keyboard is increasing, leading to recent keyboards the size of platters for serving turkey.
When we turn to reduced keyboards such as telephone keypads, the constraints governing the encoding of many symbols on few keys become much more severe. When there are many symbols on a key, some means must be provided to disambiguate the symbols, that is, to decide which symbol is intended for input. There are generically three basic approaches to disambiguating multi-symbol keys:
1) chording or shifting mechanisms, in which several keys are pressed at once, the typical example being the cap-shift key which disambiguates lower and upper case letters; 2) multi-tap mechanisms in which a key is pressed sequentially a different number of times depending on which of the symbols associated to the key is intended, telephone keypads often work this way, where the 2 key, for instance, is pressed once to input an “a”, twice to input a “b”, and three times to input a “c”; and 3) predictive-text methods in which software is used to predict which symbol is meant. An example here is the method of Riskin U.S. Pat. No. 5,031,206.
Recent advances have been made to optimally combine these methods. For instance, Gutowitz U.S. Ser. No. 09/347,188, hereby incorporated by reference, teaches an optimal method to combined a multi-tap mechanism and a predictive method. Gutowitz PCT/US99/29,343, hereby incorporated by reference, teaches a method to optimally combine a shifting mechanism with a predictive mechanism.
Extension of those teachings to the input of large symbol sets comprising digits, punctuation symbols, functional symbols, accented letters and the like, introduces a number of subtle but important problems. When the number of symbols to be encoded is very large, and the number of keys is very small, additional constraints are introduced beyond those having to do with proper disambiguation. These constraints arise due to many symbols needing to be represented on a single key. In particular, on a telephone keypad with small keys, even labelling the key with all of the symbols it needs to encode may be difficult. These problems are solved by the present invention.